WKSP

WKSP, VALUE
Automatically adds weak springs at the nodes of degrees of freedom with small or near-zero pivots during solution.

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VALUE

Spring constant, can be one of the following:

(blank)  

 — 

Default. Spring constant is internally calculated based on the underlying elements.

If positive (>0)

 — 

number entered acts as a scaling factor. Spring constant is internally calculated and then multiplied by the specified scaling factor.

If negative (<0)

 — 

User-defined spring constant. Absolute value of the specified value is used as the spring constant.

Notes

This is an action command that does the following for a non-linear anslysis that fails in the very first iteration due to a near-zero pivot error (indicating an under-constrained model):

  1. Automatically creates weak springs using COMBIN14 elements at the nodes of degrees of freedom (DOFs) with near-zero or small pivots.

  2. Retries the slution with the added springs, enhancing numerical stability and aiding convergence.

The program internally calculates a small stiffness constant (real constant 1 of COMBIN14 element) for these springs based on the average of the stiffness values of underlying elements. If you specify a positive number for VALUE, it is used as a scaling factor, and the program multiplies the internally calculated spring constant by the specified factor. If negative, the program uses the absolute value of VALUE as a customized user-defined stiffness constant. The command creates one COMBIN14 element for each translational/rotational DOF of a node where a near-zero pivot was detected by the solver in the previous failed solve.

The WKSP command does not automatically activate if the solver issues a small pivot warning and continues attempting the solution. To ensure that WKSP functions in this scenario, issue the PIVCHECK,ERROR command. This forces the solver to treat any small pivot as a fatal error and terminate the solution so that the WKSP command activates, inserts weak springs, and reattempts the stable solve.

This command is only valid when using sparse solver.

Menu Paths

This command cannot be accessed from a menu.